Stacked and trench type DRAM capacitor

ABSTRACT

A DRAM capacitor structure and its manufacturing include covering a semiconductor substrate with a first conducting layer. A first insulating layer and a second insulating layer are alternately stacked at least once above the first conducting layer to form a multi-layered structure. A contact window opening is formed in the multi-layered structure to expose a source/drain region located above the semiconductor substrate. A pattern is etch-defined on the multi-layered structure, using the first insulating layer as an etching stop layer. Part of the second insulating layer is etched away to form a cross-sectional profile similar to twin towers, with each tower having the form of a vertical T-stack. A second conducting layer covers the multi-layered structure. The first insulating layer and the second insulating layer of the multi-layered structure, as well as the second conducting layer in a top part of the multi-layered structure, are etched away to form a lower electrode. A dielectric layer is formed above the lower electrode. An upper electrode is formed above the dielectric layer.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates in general to a structure and a method of manufacturing a dynamic random-access-memory (DRAM) capacitor. More particularly, this invention relates to a structure and a method of manufacturing a stacked-type capacitor, as well as an improved combination of a stacked- and trench-type capacitor.

2. Description of Related Art

DRAM is a type of volatile memory having a signal which is stored in a digital state, depending on the charging state of the capacitor, in each memory cell. FIG. 1 is a circuit diagram of a conventional DRAM cell, which comprises a metal oxide semiconductor (MOS) transistor 11 having a gate connected to a word line (WL). One end of a source/drain region is connected to a bit line (BL), while the other end of the source/drain region is connected to ground via a capacitor 12. The digital signal of the DRAM cell is stored in the capacitor 12. The storage capacity for the digital signal increases with an increase in the charge stored in the capacitor 12. Furthermore, if the charge is increased, signal read out from the memory, using amplification circuits during a read operation, will be less affected by noise.

There are several conventional methods of increasing the charge storage capacity of a capacitor. For example, by increasing the surface area of the conducting layer in the capacitor, or by reducing the thickness of the dielectric layer in the capacitor, the amount of charge capable of being stored in the capacitor can be increased. The stacked-type capacitor, as shown in FIGS. 2 through 4, is an example of a capacitor structure having an increased capacitor area.

FIG. 2 is a cross-sectional view of a conventional stacked DRAM capacitor. First, a semiconductor substrate 20 having a MOS transistor 22, a field oxide layer 26 and a conducting layer 27 formed thereabove, is provided. The MOS transistor 22 comprises a gate 23, source/drain regions 24 and spacers 25. Then, an insulating layer 28 is deposited. This is followed by etching the insulating layer 28 to form contact openings above designated source/drain regions 24. Thereafter, a lower electrode layer 29, a dielectric layer 210 and an upper electrode layer 211 are sequentially formed above the contact window. Lower electrode layer 29, dielectric layer 210 and upper electrode layer 211 form a stacked-type capacitor 212.

The dielectric layer 210 can be a silicon nitride/silicon oxide (NO) composite layer, or a silicon oxide/silicon nitride/silicon oxide (ONO) composite layer. The lower electrode layer 29 and the upper electrode layer 211 can each be a polysilicon layer.

Finally, back-end processes, such as the formation of a metallic contact window 213 and the laying of a passivation layer (not shown in the figure), are performed to complete the fabrication of the DRAM structure.

FIG. 3 is a cross-sectional view of a second conventional stacked DRAM capacitor. First, a semiconductor substrate 30, having a MOS transistor 32, a field oxide layer 36 and a conducting layer 37 formed thereabove, is provided. The MOS transistor 32 is comprised of a gate 33, source/drain regions 34 and spacers 35. Then, an insulating layer 38 is deposited. This is followed by etching the insulating layer 38 to form contact openings above designated source/drain regions 34. Thereafter, a lower electrode layer 39, a dielectric layer 310 and an upper electrode layer 311 are sequentially formed above the contact window. Lower electrode layer 39, dielectric layer 310 and upper electrode layer 311 together form a stacked-type capacitor 312.

The dielectric layer 310 can be a silicon nitride/silicon oxide (NO) composite layer or a silicon oxide/silicon nitride/silicon oxide (ONO) composite layer. The lower electrode layer 39 and the upper electrode layer 311 can each be a polysilicon layer. Additionally, the lower electrode layer 39 has an irregular up-and-down surface profile.

Finally, back-end processes, such as the formation of a metallic contact window 313 and the laying of a passivation layer (not shown in the figure), are performed to complete the fabrication of the DRAM structure.

FIG. 4 is a cross-sectional view of a third conventional stacked DRAM capacitor. First, a semiconductor substrate 40, having a MOS transistor 42, a field oxide layer 46 and a conducting layer 47 formed thereabove, is provided. The MOS transistor 42 is comprised of a gate 43, source/drain regions 44 and spacers 45. Then, an insulating layer 48 is deposited. This is followed by etching the insulating layer 48 to form contact openings above designated source/drain regions 44. Thereafter, a lower electrode layer 49, a dielectric layer 410 and an upper electrode layer 411 are sequentially formed above the contact window. Lower electrode layer 49, dielectric layer 410 and upper electrode layer 411 together form a stacked-type capacitor 412.

The dielectric layer 410 can be a silicon nitride/silicon oxide (NO) composite layer or a silicon oxide/silicon nitride/silicon oxide (ONO) composite layer. The lower electrode layer 49 and the upper electrode layer 411 can each be a polysilicon layer. Additionally, the lower electrode layer 49 has an undulating surface profile to increase the surface area of the capacitor 412.

Finally, back-end processes, such as the formation of a metallic contact window 413 and the laying of a passivation layer (not shown in the figure), are performed to complete the fabrication of the DRAM structure.

The aforementioned stacked-type capacitor are currently the most common capacitor structures for DRAMs in use. These conventional methods all rely on improving the surface morphology of capacitors. Although the increase in surface area of the capacitor obtained by such methods increases its capacitance, the amount of such increase is limited, and is ineffective when applied to components having small dimensions.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a DRAM capacitor and a method of manufacturing the same which greatly increases the surface area of the capacitor, thus effectively raising the capacitor's capacitance.

It is yet another object of the present invention to provide a capacitor having an increased capacitance, which is suitable in applications requiring components having small dimensions.

To achieve the above objects, a DRAM capacitor and its method of manufacturing includes covering a semiconductor substrate with a first conducting layer. A first insulating layer and a second insulating layer are alternately stacked at least once above the first conducting layer to form a multi-layered structure. A contact window opening is formed in the multi-layered structure to expose a source/drain region located above the semiconductor substrate. A pattern is etch-defined on the multi-layered structure, using the first insulating layer as an etching stop layer. Part of the second insulating layer is etched away to form a cross-sectional profile similar to twin towers, with each tower having the form of a vertical T-stack. A second conducting layer covers the multi-layered structure. The first insulating layer and the second insulating layer of the multi-layered structure, as well as the second conducting layer in a top part of the multi-layered structure, are etched away to form a lower electrode. A dielectric layer is formed above the lower electrode. An upper electrode structure is formed above the dielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The description is made with reference to the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a conventional DRAM cell;

FIG. 2 is a cross-sectional view of a first conventional stacked DRAM capacitor;

FIG. 3 is a cross-sectional view of a second conventional stacked DRAM capacitor;

FIG. 4 is a cross-sectional view of a third conventional stacked DRAM capacitor;

FIGS. 5A through 5G are a series of cross-sectional views showing the manufacturing steps of a stacked DRAM capacitor, according to a first embodiment of the present invention; and

FIGS. 6A through 6G are a series of cross-sectional views showing the manufacturing steps of a DRAM capacitor according to a second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Referring to FIG. 5A, a semiconductor substrate 50 having a MOS transistor 52 is provided. MOS transistor 52 includes a gate 53 and source/drain regions 54.

As shown in FIG. 5B, a first insulating layer 55 is deposited above the semiconductor substrate 50 using the reactive gas tetra-ethyl-ortho-silicate (TEOS). The first insulating layer 55 is preferably a borophosphosilicate glass (BPSG) layer having a thickness between about 3000Å and about 6000Å.

Then, a first conducting layer 56 is deposited above the first insulating layer 55. This is followed by alternately stacking (at least once) a second insulating layer 59 and a third insulating layer 510 above the first conducting layer 56 to form a multi-layered structure 511. The first conducting layer 56 is preferably a doped polysilicon layer having a thickness between about 500 Å and about 2000 Å. The second insulating layer 59 is preferably a nitride layer having a thickness between about 2000 Å and about 5000 Å. The third insulating layer 510 is preferably a silicon dioxide layer with a thickness between about 2000 Å and about 5000 Å.

Referring next to FIG. 5C, anisotropic dry etching is used to etch the multi-layered structure 511 and form a centrally-located contact window opening 57 therein, above the source/drain region 54. Opening 57 acts as a material receiving portion. Thereafter, the multi-layered structure 511 is etched and patterned, using the first insulating layer 55 as an etching stop layer, to form the multi-layered structure 511 as a hollow cylinder.

Referring to FIG. 5D, hot phosphoric acid (H₃ PO₄) is used to wet etch and remove a portion of the second insulating layers 59, thus forming a plurality of trenches 514 on the sidewalls of the multi-layered structure 511. Trenches 514 each have depths which extend in the horizontal direction. This forms the multi-layered structure 511 with a cross-sectional profile similar to two twin towers. Each tower is in the form of a vertical stack of T's, which increases the exposed surface area of the multi-layered structure 511.

Referring next to FIG. 5E, a second conducting layer 515, for example, a doped polysilicon layer having a thickness between about 500 Å and about 2000Å, is deposited over the surface of the second insulating layer 59, the third insulating layer 510 and the exposed surface of the semiconductor substrate 50. The polysilicon layer can be formed using chemical vapor deposition, and can be doped with ions to increase its electrical conductivity.

Next, a photoresist layer (not shown in the figure) is formed above the semiconductor substrate 50. This is followed by defining a pattern to expose the profile of the multi-layered structure 511.

Subsequently, the second conducting layer 515 at a top of the multi-layered structure 511 is etched away. Then, the second insulating layer 59 and the third insulating layer 510 are sequentially etched, leaving behind only the second conducting layer 515. The second conducting layer 515 has the form of a residual shell which originally clung to the external surface of the multi-layered structure 511. The second conducting layer 515 and the first conducting layer 56 together form a lower electrode 516.

Referring to FIG. 5F, a dielectric layer 517, for example, a silicon oxide/silicon nitride/silicon oxide (ONO) composite layer, is deposited above the lower electrode 516. The ONO composite layer can be formed by first thermally growing a silicon oxide layer. Then, a silicon nitride layer is formed on top of the silicon oxide layer. Finally, a thermal oxidation process is performed to form another silicon oxide layer above the silicon nitride layer. The dielectric layer 517 typically has a thickness which is normally smaller than a thickness of the lower electrode 516. In general, the thickness of the dielectric layer 517 should not be greater than about 100 Å.

Next, an upper electrode 518, for example, a doped polysilicon layer having a thickness between about 1000 Å and about 3000 Å, is deposited above the dielectric layer 517. The upper electrode 518 is located over the lower electrode 516, and is electrically isolated from the lower electrode by the dielectric layer 517. The polysilicon layer can be formed using chemical vapor deposition, and can be doped with ions to increase its electrical conductivity.

Thereafter, the lower electrode 516, the dielectric layer 517 and the upper electrode 518 are etched to define the overall boundaries of the stacked DRAM capacitor 519.

Referring to FIG. 5G, subsequent back end processes are performed, such as depositing a fourth insulating layer 520 for planarization. This can be followed by the formation of a metal interconnect 521, so as to complete the DRAM structure according to this invention.

FIGS. 6A through 6G are a series of cross-sectional views showing the manufacturing steps of a DRAM capacitor, according to a second preferred embodiment of the present invention. This capacitor is a combination trench-type and stacked-type capacitor.

Referring to FIG. 6A, a semiconductor substrate 60 having a MOS transistor 62 is provided. MOS transistor 62 includes a gate 63 and source/drain regions 64.

As shown in FIG. 6B, a first insulating layer 65 is deposited above the semiconductor substrate 60 using the reactive gas tetra-ethyl-ortho-silicate (TEOS). The first insulating layer 65 is preferably a borophosphosilicate glass (BPSG) layer having a thickness between about 3000 Å and about 6000 Å.

Then, a first conducting layer 66 is deposited above the first insulating layer 65. This is followed by alternately stacking (at least once) a second insulating layer 69 and a third insulating layer 610 above the first conducting layer 66 to form a multi-layered structure 611. The first conducting layer 66 is preferably doped with a polysilicon layer having a thickness between about 500 Å and about 2000 Å. The second insulating layer 69 is preferably a nitride layer having a thickness between about 2000 Å and about 5000 Å. The third insulating layer 610 is preferably a silicon dioxide layer with a thickness between about 2000 Å and about 5000 Å.

Referring next to FIG. 6C, anisotropic dry etching is used to etch the multi-layered structure 511 and form a centrally-located contact window opening 67a therein, above the source/drain region 64. Opening 67a acts as a material receiving portion. Then, the etching is continued in a downward direction through the source/drain region 64 to form a first trench 67.

Thereafter, the multi-layered structure 611 is etched and patterned, using the first insulating layer 65 as an etching stop layer, to form the multi-layered structure 611 as a hollow cylinder.

Referring to FIG. 6D, hot phosphoric acid (H₃ PO₄) is used to wet etch and remove a portion of the second insulating layers 69, thus forming a plurality of trenches 614 on the sidewalls of the multi-layered structure 611. Trenches 614 each have depths which extend in the horizontal direction. This forms the multi-layered structure 611 with a cross-sectional profile similar to two twin towers. Each tower is in the form of a vertical stack of T's, which increases the exposed surface area of the multi-layered structure 611.

Referring next to FIG. 6E, a second conducting layer 615, for example, a doped polysilicon layer having a thickness between about 500 Å and about 2000 Å, is deposited over the surface of the second insulating layer 69, the third insulating layer 610 and the exposed surface of the semiconductor substrate 60. The polysilicon layer can be formed using chemical vapor deposition, and can be doped with ions to increase its electrical conductivity.

Next, a photoresist layer (not shown in the figure) is formed above the semiconductor substrate 60. This is followed by defining a pattern to expose the profile of the multi-layered structure 611.

Subsequently, the second conducting layer 615 at a top of the multi-layered structure 611 is etched away. Then, the second insulating layer 69 and the third insulating layer 610 are sequentially etched, leaving behind only the second conducting layer 615. The second conducting layer 615 has the form of a residual shell which originally clung to the external surface of the multi-layered structure 611.

Thereafter, an annealing operation is performed to activate the doped ions inside the second conducting layer 615 of the trench 67. This forms a diffusion region 68 at the bottom of the trench 67, which is the area enclosed by the dashed line in FIG. 6E. The diffusion region 68 acts as a bridge, electrically linking the electrically separated source/drain region 64, which was divided by the rift caused by the formation of the trench 67.

The second conducting layer 615 and the first conducting layer 66 together form a lower electrode 616.

Referring to FIG. 6F, a dielectric layer 617, for example, a silicon oxide/silicon nitride/silicon oxide (ONO) composite layer, is deposited above the lower electrode 616. The ONO composite layer can be formed by first thermally growing a silicon oxide layer. Then, a silicon nitride layer is formed on top of the silicon oxide layer. Finally, a thermal oxidation process is performed to form another silicon oxide layer above the silicon nitride layer. The dielectric layer 617 typically has a thickness which is normally smaller than a thickness of the lower electrode 616. In general, the thickness of the dielectric layer 617 should not be greater than about 100 Å.

Next, an upper electrode 618, for example, a doped polysilicon layer having a thickness between about 1000 Å and about 3000 Å, is deposited above the dielectric layer 617. The polysilicon layer can be formed using chemical vapor deposition, and can be doped with ions to increase its electrical conductivity.

Thereafter, the lower electrode 616, the dielectric layer 617 and the upper electrode 618 are etched to define the overall boundaries of the stacked DRAM capacitor 619.

Referring to FIG. 6G, subsequent back end processes are performed, such as depositing a fourth insulating layer 620 for planarization. This can be followed by the formation of a metal interconnect 621, so as to complete the DRAM structure according to this invention.

In summary, the manufacturing method according to the present invention has the following advantages:

(1) The multi-layered structure formed by repeatedly and alternately depositing a first conducting layer and a second insulating layer can greatly increase the surface area of the capacitor, thus greatly increasing the amount of charge capable of being stored in the capacitor.

(2) The manufacturing method has fewer steps than other conventional methods of making capacitor structures. Therefore, both production cost and production time are lower.

(3) Trench-type and stacked-type capacitor configurations can be used together in the same capacitor. This flexibility allows for a tremendous increase in the surface area of the capacitor, and hence its charge storage capacity.

While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims, which define the invention, should be accorded the broadest interpretation so as to encompass all such modifications and similar structures. 

What is claimed is:
 1. A stacked and trench-type DRAM capacitor arranged over a MOS transistor having a gate and source/drain regions, comprising:a lower electrode having a centrally located trench region which extends to the source/drain region, said lower electrode having a cross-sectional profile in the form of twin towers, each tower being a shell comprised of conductive material and having a profile of a plurality of T's stacked on top of one another in a vertical direction; a dielectric layer covering a surface of said lower electrode, and being located within the trench region and covering an interior conductive surface and an exterior conductive surface of each shell; and an upper electrode located over said lower electrode, and being electrically isolated from said lower electrode by said dielectric layer.
 2. The capacitor according to claim 1, wherein a portion of said trench region penetrates into the source/drain region, and wherein a diffusion region is formed around the portion of said trench region penetrating into the source/drain region and said dielectric layer and said upper electrode extend into the portion of said trench region penetrating into the source/drain region.
 3. The capacitor according to claim 1, wherein said lower electrode is comprised of a doped polysilicon layer.
 4. The capacitor according to claim 1, wherein said lower electrode has a thickness between about 500 Å and about 2000 Å.
 5. The capacitor according to claim 1, wherein said upper electrode is comprised of a doped polysilicon layer.
 6. The capacitor according to claim 1, wherein said upper electrode has a thickness between about 1000 Å and about 3000 Å. 